Manganese oxide compositions are inorganic compositions that may be used in industrial applications such as in (but not limited to) battery or pigment manufacturing, or that serve as precursor materials to other compositions comprising manganese. Despite their natural occurrence, manganese oxide compositions utilized in commercial applications are commonly produced by either chemical means or electrolytic means.
An example of a manganese oxide composition is manganese dioxide (MnO2). Like many inorganic compounds, manganese dioxide exists in different polymorphs or phases. Such polymorphs include, but are not limited to, α-MnO2, β-MnO2 (pyrolusite), γ-MnO2 (ramsdellite), and ε-MnO2 (akhtenskite). Polymorphs present in electrolytically synthesized MnO2 often display a high degree of crystallinity. Electrolytically synthesized MnO2 may be referred herein as “EMD”.
Another example of a manganese oxide composition is manganese (II, III) oxide, Manganese (II, III) oxide is present in nature in the mineral hausmannite, and may be used as a precursor material in the production of ceramic materials such as, but not limited to, magnets. The various chemical formulae of manganese (II, III) oxides may be generally identified as Mn3O4.
Another example of a manganese oxide composition is Mn2O3, which is present in nature in the mineral bixbyite.
Owing to the relative abundance, low toxicity, and low cost of manganese dioxide, manganese dioxide is commonly used in the production of alkaline zinc-ion batteries (e.g. alkaline Zn/MnO2 batteries); alkaline Zn/MnO2 batteries themselves occupy a significant portion of the battery market share. In general, alkaline Zn/MnO2 batteries comprise a cathode (i.e., one that comprises manganese dioxide as an cathodic active material), an anode (i.e., one that comprises zinc metal as an anodic active material), and an alkaline electrolytic solution (e.g., a potassium hydroxide solution) with which both the cathode and the anode are in fluid communication.
During operation of an alkaline Zn/MnO2 battery, zinc anodic material is oxidized, cathodic active material is reduced, and an electric current directed towards an external load is generated. Upon recharging such battery, by-products formed as a result of the reduction manganese dioxide are oxidized to re-form manganese dioxide. Products containing manganese that are produced in a typical discharge/charge cycle of a commercial Zn/MnO2 battery are described in Shoji et al., Charging and discharging behaviour of zinc-manganese dioxide galvanic cells using zinc sulfate as electrolyte, J. Electroanal. Chem., 362 (1993): 153-157.
In an alkaline Zn/MnO2 battery, it has been observed that the alkaline electrolytic environment therein contributes, over time and over a discharge/charge cycling process, to an accumulation of by-products such as, but not limited to, Mn(OH)2, Mn3O4, and Mn2O3 formed on the cathode (Shen et al., Power Sources, 2000, 87, 162). Accumulation of such by-products in Zn/MnO2 batteries may lead to undesirable consequences such as capacity fading, poor Coulombic efficiencies, or both. “Consumed” Zn/MnO2 batteries comprising such accumulated by-products are often simply discarded or recycled, and often without further consideration to the potential commercial and/or industrial utility of the accumulated by-products themselves.